Heat retrieval unit



FIG. 1 is a perspective view of a heat retrieval unit showing my design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a side elevation thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a front elevation thereof;

FIG. 6 is a side elevation taken from the side opposite that illustrated in FIG. 3; and,

FIG. 7 is a rear elevation taken opposite the front elevation of FIG. 5. 

The ornamental design for a heat retrieval unit, as shown. 